Related Party Transactions - Reimbursements from Our General Partner (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Related Party Transaction [Line Items]
Reimbursement of Zydeco directional drill	$ 3.1		$ 13.6
Refinery Gas Pipeline
Related Party Transaction [Line Items]
Reimbursement of Zydeco directional drill	0.9		1.5
Zydeco Pipeline Company LLC (“Zydeco”)
Related Party Transaction [Line Items]
Reimbursement of Zydeco directional drill	$ 2.2	$ 0.1	$ 12.1	$ 0.4
Shell Auger and Lockport Operations
Related Party Transaction [Line Items]
Reimbursement of Zydeco directional drill		$ 1.0		$ 1.2